Recently, thinning and miniaturization of a semiconductor device and its package have been increasingly demanded. Therefore, as the semiconductor device and its package, flip chip type semiconductor devices in which a semiconductor element such as a semiconductor chip is mounted (flip chip-connected) on a substrate by means of flip chip bonding have been widely utilized. In such flip chip connection, a semiconductor chip is fixed to a substrate in a form where the circuit face of the semiconductor chip is opposed to the electrode-formed face of the substrate. In such a semiconductor device or the like, there may be a case where the back surface of the semiconductor chip is protected with a protective film to prevent the semiconductor chip from damaging or the like (see, Patent Document 1). The film for back surface may be laser-marked to increase the product discrimination ability thereof (see, Patent Document 2).
Patent Document 1: JP-A-2007-158026
Patent Document 2: JP-A-2008-166451
As a typical procedure of flip chip connection, a solder bump and the like formed on a semiconductor chip surface to which a film for back surface is bonded are immersed in a flux, thereafter, the bump is brought into contact with an electrode formed on a substrate (a solder bump is further formed on the electrode as needed), and finally, the solder bump is allowed to melt to reflow connect the solder bump to the electrode. The flux has been used for the purposes of cleaning or oxidation prevention of the solder bump, improvement of solder wettability, and the like, at the time of soldering. By the procedure described above, good electrical connection between the semiconductor chip and the substrate can be formulated.
The flux is usually allowed to adhere to only the bump portion herein. However, the flux adheres to the film for back surface attached to a semiconductor chip back surface in some cases depending on working conditions. Then, when the reflow connection is performed while the flux adheres to the film for back surface, flux-derived stains occur on a surface of the film for back surface to cause a fear of deteriorating appearance properties or laser marking properties.
The invention has been made in consideration of the foregoing problem, and an object thereof is to provide a film for flip chip type semiconductor back surface, which can prevent the occurrence of stains even when a flux adheres thereto and can produce a semiconductor device having excellent appearance properties, a dicing tape-integrated film for semiconductor back surface using the same, and a method for producing the semiconductor device.
In order to solve the foregoing problem, the present inventors have made investigations. As a result, the inventors have found that a film for flip chip type semiconductor back surface, which can prevent the occurrence of flux-derived stains and can produce a semiconductor device having excellent appearance properties, can be provided by employing the following constitution, and have completed the invention.
Namely, the present invention provides a film for flip chip type semiconductor back surface, which is to be disposed on a back surface of a semiconductor element flip chip-connected onto an adherend, the film for flip chip type semiconductor back surface comprising an adhesive layer and a protective layer laminated on the adhesive layer, wherein the protective layer comprises a heat-resistant resin having a glass transition temperature of 200° C. or more or a metal.
In the film for semiconductor back surface, a layer composed of a heat-resistant resin having a glass transition temperature of 200° C. or more or a metal is formed as a protective layer, so that a flux component is finally evaporated without entering the protective layer, at reflow for flip chip bonding. As a result, the occurrence of the flux-derived stains on the film for semiconductor back surface can be prevented. The reason for such stain inhibition is estimated as follows, although it is not sure. When the flux adheres to the film for back surface having no protective layer, a molecular structure of the resin constituting the film for back surface is largely loosened at a reflow temperature. It becomes therefore easy for the flux component to enter the film for back surface, and the flux component finally remains in a state where both are partially compatible, resulting in the occurrence of the stains. On the other hand, in the film for semiconductor back surface of the invention, the protective layer composed of the heat-resistant resin having a glass transition temperature of 200° C. or more or the metal is provided. Accordingly, a micro structure (the molecular structure or an atomic structure) in the protective layer is inhibited from being loosened or not substantially loosened even at the reflow temperature, whereby the flux component is inhibited from entering the protective layer. The flux remaining on a surface of the film for semiconductor back surface is evaporated by heating at reflow. As a result, the occurrence of the flux-derived stains is prevented.
The above-mentioned heat-resistant resin is preferably at least one selected from the group consisting of a polyimide, a polyphenylene sulfide, a polysulfone, a polyether imide, a polyether ketone and a polyether ether ketone. These resins can efficiently prevent the occurrence of the flux-derived stains because of their easy availability, rigid molecular structure and extremely high glass transition temperature. Of these, polyimide is preferred as the heat-resistant resin.
The above-mentioned metal is preferably at least one selected from the group consisting of aluminum, alumite, stainless steel, iron, titanium, tin and copper. These metals can exhibit not only an effect of preventing the occurrence of the flux-derived stains, but also excellent laser marking properties.
When a surface of the above-mentioned protective layer facing the adhesive layer has been subjected to a surface activation treatment, adhesive force between the protective layer and the adhesive layer can be improved. Accordingly, both can be prevented from being peeled in production steps of a semiconductor device and at the time of use as a product after the production, and a semiconductor device having high reliability can be produced.
The above-mentioned surface activation treatment is preferably at least one treatment selected from the group consisting of a plasma treatment, an ozone water treatment, an ultraviolet ozone treatment and an ion beam treatment. By these treatments, surface activation can be efficiently performed, even when the protective layer is composed of any one of the heat-resistant resins and the metals.
The present invention further provides a dicing tape-integrated film for semiconductor back surface, which comprises: a dicing tape comprising a base material and a pressure-sensitive adhesive layer laminated on the base material, and the above-mentioned film for flip chip type semiconductor back surface, which is laminated on the pressure-sensitive adhesive layer so that the protective layer faces the pressure-sensitive adhesive layer.
In the dicing tape-integrated film for semiconductor back surface having the above-mentioned constitution, the dicing tape and the film for flip chip type semiconductor back surface are integrally formed. Accordingly, the dicing tape-integrated film of this type can be used in a dicing step of dicing a semiconductor wafer to produce a semiconductor element, and also in a subsequent picking up step. That is to say, in the case where the dicing tape is attached to a back surface of the semiconductor wafer prior to the dicing step, the above-mentioned film for semiconductor back surface can also be attached thereto, so that a step of attaching only the film for semiconductor back surface thereto (a semiconductor back surface film attaching step) is not required. As a result, the number of process steps may be reduced. Moreover, the back surface of the semiconductor wafer or the semiconductor element formed by dicing is protected by the film for semiconductor back surface with the adhesive layer. Accordingly, in the dicing step and subsequent steps (such as the picking up step), damage of the semiconductor element can be reduced or prevented, and the occurrence of the flux-derived stains at flip chip bonding can be prevented, thereby being able to produce a semiconductor device having excellent appearance properties.
The present invention furthermore provides a method for producing a semiconductor device, the method comprising: attaching a semiconductor wafer onto the film for flip chip type semiconductor back surface in the above-mentioned dicing tape-integrated film for semiconductor back surface, dicing the semiconductor wafer to form a semiconductor element, peeling the semiconductor element together with the film for flip chip type semiconductor back surface from the pressure-sensitive adhesive layer of the dicing tape, adhering a flux to a connecting member for an adherend in the semiconductor element, and flip chip-connecting the semiconductor element onto the adherend.
In the production method, the film for flip chip type semiconductor back surface on which the protective layer is formed is used, so that the occurrence of the flux-derived stains on the film for semiconductor back surface can be prevented in the flip chip bonding step, and the semiconductor device having excellent appearance properties can be efficiently produced.